This invention relates to fiber reinforced resin matrices and more particularly it relates to polyester fiber as the reinforcing fiber for a polyethylene terephthalate resin matrix. Plastic shells reinforced with fiber glass are used for certain applications such as automotive body parts or housings for tools or electronic equipment. The reinforcing fibers such as glass are cast or encapsulated in a matrix such as polyethylene terephthalate (PET) or polypropylene (PP).
There are several methods which are usually employed to form these structures. One such method uses injection molding of PET blended with a very short cut length of glass fibers. A second method uses a polyester in a solvent base which is sprayed into a mold, then laid up with glass, and then sprayed with another layer of polyester and a cross-linking agent to make this structure permanently solid. Yet in another method preform sheet is produced by consolidating (technically pre-consolidating) a mixture of glass fiber and PET or PP or by extruding PET or PP to a glass fiber mat. The sheet thus obtained is then vacuum formed or thermo-formed in a mold in a male female mold.
In all these techniques the PET has to be heated above its melting point to obtain conformance with the mold shape. Most homopolymer PET degrades very rapidly due to oxidation and hydrolytic degradation and looses it molecular weight and strength at this high temperature.
Hence, in all the above techniques, the moisture or oxygen has to be excluded from coming in contact with the hot polymer blend. This requires elaborate injection molding or blanketing or drying equipment or the use of antioxidants in the polymer.